Fourth Generation Long Term Evolution (4G LTE), proposed by the 3rd Generation Partnership Project (3GPP) standardization body, is the evolution path for existing networks such as GSM and UMTS. 4G LTE is a complete network redesign from the access network to the core network, which provides mobile broadband to mobile users. The 4G LTE access network, named the Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), utilizes multi-antenna and multiuser coding techniques to achieve unprecedented transmission speeds of 100s of Mbps on the downlink and 10s of Mbps on the uplink. The 4G LTE network core, named the Evolved Packet Core (EPC), is a flat all-IP based architecture.
The EPC core includes a Mobility Management Entity (MME), which is analogous to a Serving GPRS Support Node (SGSN) control plane from a GSM core network. The EPC core also includes a Serving Gateway (SGW), which is analogous to a SGSN data plane, and a Packet Data Network Gateway (PDN-GW, or PGW), which is analogous to a Gateway GPRS Support Node (GGSN) from a GSM network.
PGW functionality is described in 3GPP TS 23.401 for 3GPP accesses connected to the EPC via a General Packet Radio Service (GPRS) Tunneling Protocol (GTP) or Proxy Mobile IPv6 (PMIPv6, or PMIP) S5/S8 interface. The PGW also supports functionality that is common to both PMIP-based and GTP-based S5/S8 interfaces for access to the EPC via non-3GPP accesses as described in 3GPP TS 23.402.
Additionally, the PGW serves as a user plane anchor for mobility between 3GPP accesses and non-3GPP accesses to the EPC. To act as the user plane anchor, the PGW may provide Local Mobility Anchor (LMA) functionality according to the PMIPv6 specification outlined in the Internet Engineering Task Force (IETF) Request for Comments (RFC) 5213. Because the PGW serves as the LMA anchor point for user equipment (UE) PDN connections on the S5, S8, S2a, and S2b interfaces, the PGW sends and receives control plane messages in the form of Proxy Binding Update (PBU) messages and Proxy Binding Acknowledgement (PBA) messages to and from the MAGs.
Mobile nodes utilize the LMA functionality via access gateways that provide Mobile Access Gateway (MAG) functionalities according to the PMIPv6 specification. A MAG is a function on an access router that manages mobility-related signaling for a mobile node that is attached to its access link. One such access gateway operable to function as a MAG in LTE networks is the SGW, which is utilized when the mobile node is using traditional 3GPP access. However, alternative access gateways may serve as a MAG for the mobile node, such as a Wi-Fi access gateway (WAG), an Enhanced Packet Data Gateway (ePDG), a Home eNodeB Gateway (HeNB-GW), or a High-Rate Packet Data (HRPD) Serving Gateway (HSGW) in Code Division Multiple Access 2000 (CDMA2000) HRPD access networks.
PBU messages are transmitted by MAGs to LMAs in many circumstances, such as during initial UE attachment to the E-UTRAN, IPv4 address allocation by a DHCP server collocated with the PGW, UE detachment from the E-UTRAN, UE-requested additional PDN connectivity, a UE/MME/SGW-initiated PDN disconnection procedure, Intra-LTE and Inter-eNodeB handovers with SGW relocation, Inter-Radio Access Technologies (RAT) Tracking Area Update (TAU) or Radio Area Update (RAU) or Handover with SGW relocation, initial UE attachment on the S2a interface, initial attachment for chained PMIPv6-based 58-S2a/b roaming scenarios, and many other situations.
With mobile network traffic growing exponentially, service providers must be careful to manage their networks to ensure their ability to provide continued service. However, in addition to increased IP forwarding requirements, the increase of traffic has also led to a significant growth in control plane signaling load being placed on these networks. While adding additional LMA and MAG resources may help these networks scale to meet these demands, additional signaling load complexity and inefficiencies are introduced as a result.